System for transmitting and receiving short message service (SMS) messages

ABSTRACT

A system for accessing broadcast SMS messages over a wireless communication system. A base station transmits SMS messages periodically and aperiodically over a broadcast channel. The base station allocates periodic slots in the broadcast channel for each of the subscriber services providing the SMS messages and transmits slot parameters to mobile units. Using the slot parameter information, the mobile units periodically wake up to scan the broadcast channel. The period for each category of broadcast SMS messages may be different and the period may apply to a single broadcast channel. Messages arriving aperiodically can be queued and transmitted in pre-scheduled broadcast channel frames. Messages with inter-arrival interval greater than the specified transmission period are simply repeated.

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention pertains generally to the field of communications,and more particularly to the broadcast of short message service forwireless communication systems.

II. Background

In a wireless communication system, the broadcast short message service(SMS) allows the transmission of short messages from a subscriptionservice to a mobile unit. Generally, broadcast SMS messages are messagesassociated with services subscribed to by a user. Broadcast SMS cancomprise entry features, administration features, or informationmessages. For example, a subscriber may subscribe to a stock quotesservice wherein the subscriber will receive stock quotes on a wirelessdevice or a mobile unit, such as a personal data assistant (PDA), laptopcomputer, a cellular telephone or a PCS telephone, from a subscriptionservice utilizing the wireless communication system.

Various over-the-air interfaces have been developed for wirelesscommunication systems including, e.g., frequency division multipleaccess (FDMA), time division multiple access (TDMA), and code divisionmultiple access (CDMA). In connection therewith, various domestic andinternational standards have been established including, e.g., AdvancedMobile Phone Service (AMPS), Global System for Mobile Communications(GSM), and Interim Standard 95 (IS-95).

An exemplary wireless telephony communication system is a code divisionmultiple access (CDMA) system. The IS-95 standard and its derivatives,IS-95A, IS-95B, IS-2000, proposed high-data-rate CDMA standardsexclusively for data, etc. (referred to collectively herein as IS-95),are promulgated by the Telecommunication Industry Association (TIA) andother well known standards bodies to specify the use of a CDMAover-the-air interface for cellular or PCS telephony communicationsystems. Exemplary wireless communication systems configuredsubstantially in accordance with the use of the IS-95 standard aredescribed in U.S. Pat. Nos. 5,103,459 and 4,901,307, which are assignedto the assignee of the present invention and fully incorporated hereinby reference.

A problem arises when a broadcast SMS message is transmitted over thewireless communication system. The mobile units that are subscribers tothe subscription service must acquire the broadcast SMS message in atimely manner, but in order to do so, the mobile units must be awakenedfrom an idle state. The process of “waking up” from the idle state,demodulating the SMS message broadcast from a base station, and thenreturning to the idle state involves a power drain on each mobile unit'sbattery that can measurably diminish the power level of the mobileunit's battery. The length of time in which the mobile unit spends awakeis approximately proportional to the power consumption of the mobileunit.

Hence, there is a present need to minimize the total battery drain ofthe mobile unit while allowing the mobile unit to detect and processbroadcast SMS messages in a timely manner.

SUMMARY

The present invention is directed to a method for transmitting andreceiving broadcast SMS messages over a broadcast channel in a wirelesscommunication system, comprising the steps of: generating a parametermessage to be broadcast from a base station to a mobile unit, whereinthe parameter message contains a set of transmission parameters for thebroadcast channel; processing the parameter message at the mobile unit;and setting a periodic wake up schedule for the mobile unit inaccordance with the set of transmission parameters, wherein the mobileunit wakes up periodically in order to detect a broadcast SMS message inone or more assigned broadcast channel frames. The period for eachcategory of broadcast SMS messages may be different and the period mayapply to a single broadcast channel. Messages arriving aperiodically canbe queued and transmitted in pre-scheduled broadcast channel frames.Messages with inter-arrival interval greater than the specifiedtransmission period are simply repeated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a cellular telephone system.

FIG. 2 is a block diagram of a processor and associated memory elementsused to generate a transmission parameter message.

FIG. 3 is a flow chart of one embodiment of the invention.

FIG. 4 is a timeline of transmission periods for a broadcast channel.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention pertains to a system for transmitting SMS messageson a broadcast channel. An exemplary wireless communication system inwhich the present invention is embodied is illustrated in FIG. 1. In apreferred embodiment, the communication system is a CDMA wirelesscommunication system, although it should be understood that the presentinvention is equally applicable to other types of communication systems.Systems utilizing other well-known transmission modulation schemes suchas TDMA and FDMA as well as other spread spectrum systems may employ thepresent invention.

As illustrated in FIG. 1, a CDMA wireless telephone system generallyincludes a plurality of mobile subscriber units 10, a plurality of basestations 12, base station controllers (BSCs) 14, and a mobile switchingcenter (MSC) 16. The MSC 16 is configured to interface with aconventional public switch telephone network (PSTN) 18. The MSC 16 isalso configured to interface with the BSCs 14. The BSCs 14 are coupledto the base stations 12 via backhaul lines. The backhaul lines may beconfigured to support any of several known interfaces including, e.g.,E1/T1, ATM, IP, PPP, Frame Relay, HDSL, ADSL, or xDSL. It is understoodthat there may be more than two BSCs 14 in the system. Each base station12 advantageously includes at least one sector (not shown), each sectorcomprising an omnidirectional antenna or an antenna pointed in aparticular direction radially away from the base station 12.Alternatively, each sector may comprise two antennas for diversityreception. Each base station 12 may advantageously be designed tosupport a plurality of frequency assignments. The intersection of asector and a frequency assignment may be referred to as a CDMA channel.The base stations 12 may also be known as base station transceiversubsystems (BTSs) 12. Alternatively, “base station” may be used in theindustry to refer collectively to a BSC 14 and one or more BTSs 12. TheBTSs 12 may also be denoted “cell sites” 12. Alternatively, individualsectors of a given BTS 12 may be referred to as cell sites. The mobilesubscriber units 10 are typically cellular or PCS telephones 10. Thesystem is advantageously configured for use in accordance with the IS-95standard.

During typical operation of the cellular telephone system, the basestations 12 receive sets of reverse link signals from sets of mobileunits 10. The mobile units 10 are conducting telephone calls or othercommunications. Each reverse link signal received by a given basestation 12 is processed within that base station 12. The resulting datais forwarded to the BSCs 14. The BSCs 14 provides call resourceallocation and mobility management functionality including theorchestration of soft handoffs between base stations 12. The BSCs 14also routes the received data to the MSC 16, which provides additionalrouting services for interface with the PSTN 18. Similarly, the PSTN 18interfaces with the MSC 16, and the MSC 16 interfaces with the BSCs 14,which in turn control the base stations 12 to transmit sets of forwardlink signals to sets of mobile units 10.

In accordance with the exemplary wireless communication system, FIG. 2shows a mechanism 100 for generating a transmission parameter messageincluding a processor 102, a software module 104, and a storage medium106. The processor 102 is advantageously a microprocessor or aspecial-purpose processor such as a digital signal processor (DSP), butmay in the alternative be any conventional form of processor,controller, microcontroller, or state machine. The processor 102 iscoupled to the software module 104, which is advantageously implementedas RAM memory holding software instructions that direct the operation ofthe processor 102. The software instructions can comprise a softwareprogram or a set of microcodes. The RAM memory 104 may be on-board RAM,or the processor 102 and the RAM memory 104 could reside in an ASIC. Inan alternate embodiment, firmware instructions are substituted for thesoftware module 104. The storage medium 106 is coupled to the processor102, and is advantageously implemented as a combination of RAM memoryand any form of conventional nonvolatile memory such as, e.g., ROMmemory. The storage medium 106 is used to store precomputed tables andinstructions. For example, the instructions and tables are stored in theROM memory component while the register is stored in the RAM memorycomponent. In the alternative, the storage medium 106 could beimplemented as either a disk memory or a flash memory that is accessibleby the processor 102. In the alternative, the storage medium 106 may beimplemented as registers. The mechanism 100 may reside in anyconventional communications device such as, e.g., the mobile subscriberunits 10 or the base stations 12 in the CDMA wireless telephone systemof FIG. 1.

FIG. 3 is a block diagram illustrating an embodiment of the invention,wherein SMS messages are broadcast periodically or aperiodically from abase station throughout the base station's coverage area. At step 300, abase station receives subscriber service information from subscriberservices. It should be understood that the base station may receiveinformation from subscriber services at any time. At step 310, a mobileunit enters the coverage area of a base station and acquires systemparameters from the base station. System parameters include subscriberservice transmission parameters that define the wake up schedule formobile units that have subscribed to a subscription service. At step320, the mobile unit processes the subscriber service transmissionparameters and sets an internal wake up schedule accordingly. At step330, the mobile unit begins to follow the internal wake up schedule,wherein the mobile unit wakes up from an idle state to periodically scanthe broadcast channel for SMS messages. The method described herein isrepeated each time a mobile unit enters the coverage area of a new basestation. It is understood that all base stations in the wirelesscommunication system will be receiving the subscriber serviceinformation from subscriber services.

The subscriber service transmission parameter message from the basestation may be transmitted periodically or aperiodically to the mobileunits that are subscribers to a service in the coverage area. Thesubscriber service transmission parameter message instructs the mobileunits when to wake up from an idle state, demodulate the SMS messagethat may be carried on the broadcast channel, and when to return to anidle state while the mobile units remain in the coverage area of thebase station. Table 1 contains some of the specific parameters that maybe transmitted by the base station.

TABLE 1 Parameter Units # of Bits Message Category N/A 16  MinimumTransmission Period (MTP) 1.28 sec. intervals 8 Transmission Period MTPs9 or 11 Transmission Offset from System Time BCCH frames Up to 13 in theMinimum Transmission Period Transmission Offset from System Time MTPs 9or 11 in the Transmission Period Number of Repetitions N/A 2 SeparationBetween Repetitions MTPs 2 Burst Length BCCH frames 10 

System time is the time reference used by the base station and issynchronous to Universal Coordinated Time (UTC), which is aninternationally agreed-upon time maintained by the Bureau Internationalde l'Heure (BIH). Values are assigned to the parameters that correspondto the desired broadcast schedule of each service. The MinimumTransmission Period (MTP) parameter specifies the cycle duration inunits of 1.28 seconds. The numerical value of 1.28 seconds is theminimum slot cycle for mobile stations operating in the slotted modeaccording to IS-95. However, it should be understood that this numericalvalue could be modified without limiting the scope of this invention.

The Transmission Period Parameter is defined in units of MTP and can beset so that transmission periods will occur up to a maximum limit of aday (9 bits) or a week (11 bits), according to system parameters. TheTransmission Period parameter can be determined from the average ormaximum rate at which new messages arrive. For example, if a SMS messagefrom a subscription service arrives at the base station once every 15minutes, then the Transmission Period for the slot assigned to thatsubscription service should be set to be less than or equal to 15minutes.

The Transmission Offset from System Time in the MTP parameter is definedin units of broadcast channel (BCCH) frames and is used to identifywhich slot in the MTP is assigned to a specific service. TheTransmission Offset from System Time in the Transmission Periodparameter is defined in units of MTP and is used to identify which slotin the transmission period is assigned to a specific service. TheSeparation Between Repetitions parameter is defined in units of MTP.Repeated transmissions with short separation are used to supportservices that have very long transmission periods. Burst Length isdefined in units of BCCH frames and is used to support messages that arelonger than a broadcast channel frame.

Using these specific parameters, a base station can choose an arbitraryminimum transmission period that can be divided into slots correspondingto the broadcast channel frames, which may be 40 ms, 80 ms, or 160 mslong or as otherwise defined. The base station can transmit broadcastSMS messages on the broadcast channel repeatedly, with repetitions ofthe broadcast SMS message sent in consecutive frames, or in framesseparated by a fixed time interval. The transmission schedule that istransmitted from the base station to the mobile unit gives the mobileunit the ability to power up for those prearranged times when abroadcast SMS message is to be transmitted. In addition, thetransmission schedule gives the base station flexibility in structuringthe SMS message.

Using the subscriber service transmission parameters, a mobile unit canscan for specific SMS messages over assigned slots in the broadcastchannel. For example, FIG. 4 is a timeline of exemplary transmissionperiods over a broadcast channel, wherein the broadcast SMS messages arestructured flexibly. The length of the broadcast SMS message can be afraction of the length of a broadcast channel frame, the length of abroadcast channel frame, or a multiple of the length of a broadcastchannel frame. The transmission period for service A 410 is equal to theminimum transmission period 401. The transmission period 402 forservices B 410, C 430, and D 440 is twice the minimum transmissionperiod 401. The transmission period 403 for services E 450, F 460, G470, H 480, and I 490 is four times the minimum transmission period 401.Each message for services A 410 through H 480 has the duration of onebroadcast channel frame 404 and each message for service I 490 spansover two broadcast channel frames.

For those messages from subscriber services that may not be previouslyscheduled, i.e., emergency news or breaking news stories, the basestation may have a designated service slot that remains empty duringregular periods, but can be used to carry unscheduled SMS messages atappropriate times.

In another embodiment of the invention, the minimum transmission periodof the broadcast channel frames can be arbitrarily lengthened toincrease the subscriber service capacity of the wireless communicationsystem. In wireless devices that are broadcast SMS enabled only, i.e.,laptaps, PDAs, pagers, and other data devices, the necessity of constantscans for incoming voice calls is eliminated. In cellular and PCS mobilephones with data capabilities, the service configuration between thebase station and the mobile phone unit include service options for bothvoice and SMS messages (data). Because of the voice service option, theslot cycle for most systems have been set to 1.28 seconds or 2.56seconds, which would allow mobile units to detect the presence ofincoming voice calls in a timely manner. Longer periods increase theprobability that a calling party will disconnect the phone call beforethe mobile unit detects the signal or the mobile unit can notify theuser.

However, in wireless devices that are not voice-enabled, the constraintof a short slot cycle is essentially eliminated. The base station canlengthen the minimum transmission period arbitrarily so that broadcastSMS messages can be scheduled for transmission once a week, or once aday, or once every 1.28 seconds. The alteration of the minimumtransmission period can change the service capabilities of the mobileunit. For example, if all services are transmitted at a rate of onemessage every 32 seconds, and each message lasts for one 160 msbroadcast channel frame, then 200 services can be supported in that 32second period. However, if services are transmitted at a rate of onemessage every 1.28 seconds, and each message lasts for one 160 msbroadcast channel frame, then only 8 services can be supported in the1.28 second period.

In general, let the minimum transmission period be m×1.28 seconds,wherein m is chosen such that 1≦m≦256 and the broadcast channel framelength be k×40 ms, wherein k=1, 2, or 4. Then there are 32m/k broadcastchannel frames in each minimum transmission period. If each message isone frame long, then these 32m/k frames can be used to transmit either:

1. a set of 32m/k messages with the transmission period equal to theminimum transmission period, or

2. a set of 64m/k services with transmission period twice as long as theminimum transmission period, or

3. a combination of 16m/k services with transmission period equal to theminimum transmission period and 32m/k services with transmission periodtwice as long as the minimum transmission period.

Preferred embodiments of the present invention have thus been shown anddescribed. It would be apparent to one of ordinary skill in the art,however, that numerous alterations may be made to the embodiments hereindisclosed without departing from the spirit of scope of the invention.Therefore, the present invention is not to be limited except inaccordance with the following claims.

I claim:
 1. A method for transmitting and receiving Short MessageService (SMS) messages over a broadcast channel in a spread spectrumsystem, wherein the SMS messages originate from a plurality ofsubscription services, comprising the steps of: generating a parametermessage to be transmitted from a base station to a mobile unit, whereinthe parameter message contains a set of SMS transmission parameters forthe broadcast channel; processing the parameter message at the mobileunit; and setting a periodic wake up schedule for the mobile unit inaccordance with the set of SMS transmission parameters, wherein themobile unit wakes up periodically in order to detect a broadcast SMSmessage in one of a plurality of broadcast channel frames; wherein theset of SMS transmission parameters comprises: a minimum transmissionperiod, wherein the minimum transmission period is variable; atransmission period, wherein the transmission period has a duration thatis a multiple value of the minimum transmission period, and wherein thetransmission period is variable; a minimum transmission period offset,wherein the minimum transmission period offset directs the mobile unitto demodulate a specified broadcast channel frame during the minimumtransmission period; and a transmission period offset, wherein thetransmission period offset directs the mobile unit to demodulate aspecified broadcast channel frame during the transmission period;wherein the transmission period has a value greater than or equal to aSMS message arrival rate, wherein the SMS message arrival rate is therate at which the base station receives information from at least one ofthe plurality of subscriber services.
 2. The method of claim 1, whereinat least one of the plurality of broadcast channel frames is reservedfor an aperiodic SMS message.
 3. A method for transmitting and receivingShort Message Service (SMS) messages over a broadcast channel in aspread spectrum system, wherein the SMS messages originate from aplurality of subscription services, comprising the steps of:transmitting a plurality of parameter messages over the broadcastchannel, wherein each of the plurality of parameter messages contains aset of SMS transmission parameters; processing the plurality ofparameter messages at the mobile unit; and setting a periodic wake upschedule for the mobile unit in accordance with each of the sets of SMStransmission parameters, wherein the mobile unit wakes up periodicallyin order to detect a SMS message in one of a plurality of broadcastchannel frames; wherein each of the set of SMS transmission parameterscomprises: a minimum transmission period, wherein the minimumtransmission period is variable; a transmission period, wherein thetransmission period has a duration that is a multiple value of theminimum transmission period, wherein the transmission period has a valuegreater than or equal to a SMS message arrival rate, wherein the SMSmessage arrival rate is the rate at which the base station receivesinformation from at least one of the plurality of subscriber services,and wherein the transmission period is variable; a minimum transmissionperiod offset, wherein the minimum transmission period offset directsthe mobile unit to demodulate a specified broadcast channel frame duringthe minimum transmission period; and a transmission period offset,wherein the transmission period offset directs the mobile unit todemodulate a specified broadcast channel frame during the transmissionperiod.
 4. The method of claim 3, wherein at least one of the pluralityof broadcast channel frames is reserved for an aperiodic SMS message. 5.An apparatus for transmitting and receiving Short Message Service (SMS)messages over a broadcast channel in a spread spectrum system, whereinthe SMS messages originate from a plurality of subscription services,comprising: means for generating a parameter message to be transmittedfrom a base station to a mobile unit, wherein the parameter messagecontains a set of SMS transmission parameters for the broadcast channel;means for processing the parameter message at the mobile unit; and meansfor setting a periodic wake up schedule for the mobile unit inaccordance with the set of SMS transmission parameters, wherein themobile unit wakes up periodically in order to detect a broadcast SMSmessage in one of a plurality of broadcast channel frames; wherein theset of SMS transmission parameters comprises: a minimum transmissionperiod, wherein the minimum transmission period is variable; atransmission period, wherein the transmission period has a duration thatis a multiple value of the minimum transmission period, and wherein thetransmission period is variable; a minimum transmission period offset,wherein the minimum transmission period offset directs the mobile unitto demodulate a specified broadcast channel frame during the minimumtransmission period; and a transmission period offset, wherein thetransmission period offset directs the mobile unit to demodulate aspecified broadcast channel frame during the transmission period;wherein the transmission period has a value greater than or equal to aSMS message arrival rate, wherein the SMS message arrival rate is therate at which the base station receives information from at least one ofthe plurality of subscriber services.
 6. The apparatus of claim 5,wherein at least one of the plurality of broadcast channel frames isreserved for an aperiodic SMS message.
 7. An apparatus for transmittingand receiving Short Message Service (SMS) messages over a broadcastchannel in a spread spectrum system, wherein the SMS messages originatefrom a plurality of subscription services, comprising: means fortransmitting a plurality of parameter messages over the broadcastchannel, wherein each of the plurality of parameter messages contains aset of SMS transmission parameters; means for processing the pluralityof parameter messages at the mobile unit; and means for setting aperiodic wake up schedule for the mobile unit in accordance with each ofthe sets of SMS transmission parameters, wherein the mobile unit wakesup periodically in order to detect a SMS message in one of a pluralityof broadcast channel frames; wherein each of the set of SMS transmissionparameters comprises: a minimum transmission period, wherein the minimumtransmission period is variable; a transmission period, wherein thetransmission period has a duration that is a multiple value of theminimum transmission period, wherein the transmission period has a valuegreater than or equal to a SMS message arrival rate, wherein the SMSmessage arrival rate is the rate at which the base station receivesinformation from at least one of the plurality of subscriber services,and wherein the transmission period is variable; a minimum transmissionperiod offset, wherein the minimum transmission period offset directsthe mobile unit to demodulate a specified broadcast channel frame duringthe minimum transmission period; and a transmission period offset,wherein the transmission period offset directs the mobile unit todemodulate a specified broadcast channel frame during the transmissionperiod.
 8. The apparatus of claim 7, wherein at least one of theplurality of broadcast channel frames is reserved for an aperiodic SMSmessage.